Organic materials, whether natural or synthetic, are conventionally protected against degradation by ultraviolet (UV) light by incorporating a UV light stabilizer in the materials. Many classes of compounds are known to be useful UV light stabilizers, some being more effective than others. Particularly effective compounds, which provide compositions resistant to degradation by UV light, include the 2-keto-1,4-diazacycloalkanes disclosed in my copending U.S. patent application Ser. No. 835,065 to be issued as U.S. Pat. No. 4,190,571.
Several syntheses of 2-keto-1,4-diazacycloalkanes with various substituents on the diaza ring are disclosed in my copending U.S. patent application Ser. No. 916,640 now issued as U.S. Pat. No. 4,167,512. In one synthesis (referred to as "the cyanohydrin synthesis") a cyclic or acyclic 1,2-diamine is reacted with an acyclic or cyclic cyanohydrin in the presence of a suitable organic solvent, and in the presence of solid or aqueous NaOH at ambient temperature and pressure, in the presence of an onium salt phase transfer catalyst in conjunction with a haloform.
In my copending patent application Ser. No. 057,238, and in said U.S. Pat. No. 4,167,512, a synthesis (referred to as "the ketoform synthesis") is disclosed in which a preselected 1,2-diamine is reacted with a saturated acyclic or cyclic monoketone, and, a haloform, in the presence of (i) a phase transfer catalyst (ii) an organic solvent, and (iii) solid or aqueous alkali. The phase transfer catalyst is selected from the group consisting of a tertiary or quaternary compound of an element selected from Groups VA and VIA of the Periodic Table, and, a polyether. Polyether phase transfer catalysts are especially noteworthy for their highly directive effect, that is, their ability to direct substituents on to the N.sup.4 -adjacent C atoms which are the more desirable positions of a diaza ring, so that polysubstituted compounds so formed exhibit exceptional UV light stability. The "soft ion synthesis" of this invention, in which, as in the ketoform synthesis, the presence of a monoketone or monoaldehyde is essential, a "soft ion", described hereinbelow, further enhances the directivity of the ketoform synthesis.
The substituted 2-keto-1,4-diazacycloalkanes with dialkyl substituents on each of two N.sup.4 -adjacent carbon ("C") atoms (also referred to as "symmetrical C atoms") are particularly effective u-v light stabilizers, having been generally found to be more effective than isomers in which the same substituents are otherwise substituted, that is, one N.sup.4 -adjacent atom of the isomer's diaza ring is unsubstituted. Though all isomers having plural substituents on the diaza ring are referred to herein as being polysubstituted, the more desirable isomers have substituents on each N.sup.4 -adjacent C atom of the diaza ring. The less desirable (because they are less effective as u-v stabilizers) isomers have an unsubstituted N.sup.4 -adjacent C atom. This invention is directed to a synthesis in which a "soft ion" catalyst is used to produce a directive effect, and thus favorably direct or bias the formation of the more desirable isomer at the expense of the less desirable one.